Effect of curing period and RAP content on properties of foamed bitumen-stabilised material

Foamed bitumen-stabilised material (BSM) is an economical and environmentally sustainable mixture that provides a robust and durable base course in pavement construction, contributing to sustainable infrastructure development. Owing to the heterogeneous nature of the constituents within the BSM matrix, a detailed understanding of their complex interactions is essential. This study investigated the combined effects of foamed bitumen (FB) content, reclaimed asphalt pavement (RAP) and curing duration on BSM's volumetric and mechanical properties using statistical methods. It also applies the Michaelis‒Menten (M.M.) model to characterise curing kinetics and provides deeper insight of its evolving behaviour. It was observed that curing duration most strongly influences the mechanical strength property, surpassing the effects of the FB content and RAP. RAP influences both volumetric and mechanical properties more than FB, highlighting the need for modified aggregate gradation rather than relying exclusively on 100% RAP usage to meet BSM 1 strength criteria (ITS ≥ 225 kPa), however mixes with 100% RAP exceed the thresholds (ITS ≥ 175 kPa) to meet the BSM 2 strength criteria set by the Asphalt Academy (TG2). The optimal FB content was found to be 2.5% across all mix variants. ITS‒moisture loss correlation enables non-destructive ITS prediction at varying moisture levels. The M.M. model accurately forecasts curing parameters, which helps in optimising material selection and mix design.